The present invention relates to an apparatus for forming a bump and bonding it to a substrate with uniform and sufficient strength. Such bumps are used to mount semiconductor devices or optical devices on a substrate.
In the high density semiconductor devices mounting art, as well as in optical devices mounting art, use is made of flip chip bonding which bonds a device and a substrate via minute bumps and can reduce module size. As for semiconductor devices, flip chip bonding allows bonding points to be arranged in a higher density than wire bonding, TAB (Tape Automated Bonding) and other bonding technologies, thereby increasing packaging density and reducing apparatus size. Another advantage available with flip chip bonding is that when a bump is caused to reflow, an accurate bonding position is achievable due to a self-alignment effect which is derived from the surface tension of the melted bump. Therefore, when an optical device is mounted on a substrate, it is not necessary to adjust the optical axis of the device and those of a waveguide, optical fiber and other optical parts. This successfully reduces the mounting cost of optical modules and, therefore, the cost of optical modules.
When a semiconductor device or an optical device is to be mounted on a substrate by flip chip bonding, it is necessary to form bumps on one or both of the substrate and device. To form bumps, electrode pads provided on a substrate may be subjected to plating, vapor deposition, sputtering, solder paste printing or transfer bump procedure by way of example. On the other hand, a procedure capable of forming bumps on the desired positions of a substrate rapidly without resorting to a time-consuming vacuum process is also available. This kind of procedure punches a thin ribbon-like metallic material with a punch and a die and then directly bonds, with the remaining force, the resulting bump to a substrate by thermo-compression, as taught in, for example, Japanese Patent Laid-Open Publication Nos. 4-65847 and 4-152682.
The prerequisite with the above punching scheme is that bumps be stamped out from the ribbon in a constant volume at all times. Another prerequisite is that the bumps be bonded to a substrate by suficient strength while being prevented from chipping off or cracking. However, the conventional punching procedure is apt to cause bumps to chip off or crack when they are stamped out from a substrate, so that uniform bumps are not attainable.